Device and method for recording sound waves



Nov. 29, 1932. s. RUBEN 1,889,380

DEVICE AND METHOD FOR RECORDING SOUND WAVES Filed July 14, 1951 INVENTORSAMUEL RUBEN BY HIS ATTORNEY W Patented Nov. 29, 1932 SAMUEL RUBEN, NEWROCHELLE, NEW YORK DEVICE AND METHOD FOR RECORDING SOUND WAVESApplication filed July 14,

This invention relates to a device and method for recording sound waves,and more particularly, it relates to an electro-magnetlc means forrecording oscillations of audio frequencies by electro-magnetically ormechanically transposing magnetically permeable particles suspended in amixture upon a supporting element.

In the prior art much experimentation has been conducted to magneticallyrecord audio frequency oscillations upon a steel wire by passing itthrough a magetic field, the potential of which is varied throughoscillations impressed upon the field, recording being effected throughmolecular transposition. This system has several limitations, such aslow intensity of reaction and an impermanent effect. By my inventionthese limitations are reduced and the magnetic recording is accom- 0plished without any molecular change in a metal wire; there is a morepositive effect which permits recording of greater intensity andpermanency.

I have found that when a magnetically permeable material, such as finelydivided ferro-ferric oxide (Fe O is thoroughly blended in a mixture,such as that of shellac and Venice turpentine, it remains in perfect anduniform suspension, and that the oxide particles within the mixture aretransposed under varying electrical field influences when the mixture isfiuxed or in a plastic state. For recording purposes the mixture isapplied as a coating upon a flexible wire or strip, as soft iron orcopper, which is preferably passed through the fluid mixture, thecoating being then baked, becoming a smooth black enamel. Heated,preferably by induction, to about 70 C. the coating becomes plastic, andin this state is passed through a magnetic field of varying flux, thesmall permeable particles within a limited area, aligning themselvesaccording to the varying field characteristics. The permeability of thecoated strip is varied by electro-magnetically moving the iron oxideparticles and fixing them in their new positions. Through varying themagnetic flux by oscillations impressed upon the controlling field froma source of electrical oscillations, such as a microphone circuit, thenewly 1931. Serial No. 550,707.

assumed positions are determined by the frequencles and intensities ofthose oscillations. It is of advantage to restrict the magnetic field asfar as practicable to the area occupied by the coated strip in itspassage between the poles; this may be accomplished as by tapering themagnet poles, though such a step 1s not necessary if a soft iron wire orstrip be employed as the base for the coating. By prompt cooling by airblast or other cool- 0 mg means, the magnetic particles are permanentlyset in their new positions. However, if the field variations are of verygreat intensity, the permeable particles can be sufiicient- 1yre-aligned without the heating or cooling. 5

If audio frequency oscillations are so impressed upon the coating, as bymodulating a static magnetic field, as the coated strip is passedthrough the field, there are definite movements of the oxide particlescorres onding to the magnetic field modulations. ith the particles fixedin their new positions the coated strip, on being passed through amagnetic field connected with a translating device, such as a telephonereceiver capable of responding to induced potential caused by changes inthe permeability of the magnetic particles, reproduction of the originaloscillation recording is effected.

For the suspension or binding mixture, that described is preferred, butany organic or inorganic binder permitting the movement of suspendedmagnetically permeable particles and adapted to quick hardening may besubstituted. Iron oxide of the magnetic oxide type (Fe 0 has been foundhighly satisfactory because, unlike iron dust and various otherpermeable materials, it remains more evenly distributed in thesupporting mixture. And because of its high permeability, soft iron wireis a desirable base for the coating; however, other materials of greateror less permeability than iron can be applied for, unlike the steel wireof the earlier magnetic recording systems, the core itself has nofunction other than that of a mechanical support for the coating; thatis, there is no molecular transposition or any other effect in the wiresupport; it is readily permeated by the magnetic lines of force.

. tween roller 4. and needle 4 the latter at It is apparent that thecoating, while in a plastic state, can also be subjected to mechanicalimpacts at audio frequencies which likewise transpose the particleswithin the coating. But the method of magnetically transposing themagnetically permeable particles is considered preferable to amechanical method, due to the reduction of inertia. Reproduction of theoscillations so impressed may be effected in the manner above described.

For efi'acing the record, the coated wire is heated and then passedthrough an intense constant electrical field, by means of which thetransposed oxide particles resume their normal positions; that is, theyare uniformly distributed throughout the coating mixturewhich is thencooled.

Amplification can be obtained through the employment of the meansusually adopted for this purpose.

For a better understanding of the invention reference is made to theaccompanying drawing of an embodiment of the invention in which Fig. 1diagrammatically illustrates the magnetic recording system, Fig. 2, thereproducing system and Fig. 3, a recording system employing amagnetically controlled needle or the like for mechanically changing theposition of the magnetic particles.

Referring more in detail to Fig. 1, A and C respectively representspools from which and upon which is wound iron wire 1, coated with amixture of shellac, Venice turpentine and minute particles offerro-ferric oxide. The wire coating is made plastic by heater element2, current for which is supplied by source 3, before passing between thepoles of electro-magnet 4, after which the coated wire with themagnetically permeable particles transposed, passes through coolingsolution 5, in container 6, and around immersed spool B. Upon magnet 4,is mounted coil 7, in circuit with energy source 9, and microphone 8.

In Fig. 2, the coated wire 1, upon which the oxide particles transposedby the recording operation through the impression of oscillations uponthe field, is passed between magnet poles 4, from spool A to spool C.Upon the magnet 4, is wound coil 7 in circuit with telephone receiver10, the induced energy in that circuit being modified in accordance withthe changes in the magnetic field corresponding to the recordedoscillations on the coated wire as it passes through the field.

The elements in Fig. 3 bearing the same numbers, correspond with likeelements in Fig. 1. In this system the oxide particles are transposed bymechanical means rather than directly by magnetic influence; the wirecoated with the plastic mixture is passed betached to movable armature4., of magnet 4. With the density of the magnetic field varyingresponsively to audio frequency oscillations impressed upon microphone8, tin circuit with coils 7 the movable armature 4. varies the pressureof needle 4,, against the plastic coating, mechanically causing thetransposition of the oxide particles in the coating. The movement of thearmature with audio frequency oscillations impressed upon the microphonecircuit and the pressure of the needle against the face of the plasticcoating causes corresponding undulations in the coated surface, which isthen cooled.- The same cooling means as that shown in Fig. 1 isemployed. The permeable oxide particles are thus fixed in their changedpositions, the sound waves being then reproduced by the passage of thecoated strip through a mag-' netic field, the oscillations in whichserve to modulate the current in the receiver circuit.

What I claim is: 1. The method of recording audio frequency oscillationswhich consists in varying the intensity of the field of anelectromagnet, by impressing electrical oscillations transposing saidparticles by impressing electrical oscillations of audio frequency upona circuit controlling the intenslty of said field, and in cooling themixture while the particles are in said transposed state.

3. The method of recording audio frequency oscillations which consistsin passing a metal strip having a plastic coating containingmagnetically permeable particles', through the field of anelectro-magnet, electromagnetically charging and transposing saidparticles by impressing electrical oscillations of audio frequency upona circuit controlling the intensity of said field, and hardening thecoating while the particles are so transposed.

4. The method of recording audio frequency oscillations which consistsin pass ing through the field of an electro-magnet, a metal strip coatedwith a plastic mixture containing ferro-ferric oxide particles, andtransposing the particles by varying the intensity of the field of saidelectro-magnet by impressing upon the circuit controlling said fieldelectrical oscillations of audio frequency.

5. The method of recording audio frequency oscillations which consistsin fluxing a mixturecoated upon a magnetically permeable metal stripcontaining ferro-ferric oxide, passing the mixture through the field ofan electro-magnet, transposing particles of said ferro-ferric oxidematerial by varying the intensity of said field by impressing electricaloscillations of audio frequency upon the circuit controlling theintensity of said field and in cooling the mixture while the particlesof said oxide are in said transposed state.

6. A device for recording audio frequency oscillations comprising anelectro-magnet, a circuit for controlling the field of the magnet, meansfor passing through said field a metal strip coated with a semi-fluidbinder containing magnetically permeable particles, and means fortransposing said particles at right angles to the metal strip within thebinder by impressing audio frequency oscillations upon said circuit.

7. A device for recording audio frequency oscillations comprising anelectro-magnet, a circuit for controlling the field of the magnet, meansfor passing through said field an iron Wire strip coated with a semifluid binder containing magnetically permeable particles, and means fortransposing said particles within the binder by impressing audiofrequency oscillations upon said circuit.

8. A device for recording audio frequency oscillations comprising anelectro-magnet, a circuit for controlling the field of the mag net,means for passing through said field a metal strip coated with asemi-fluid binder containing ferro-ferric oxide particles, and means fortransposing said particles within the binder by impressing audiofrequency oscillations upon said circuit.

9. A device for recording audio frequency oscillations comprising anelectro-magnet, a circuit for controlling the field of the magnet, meansfor passing through said field a metal strip coated with a bindercontaining magnetically permeable particles, means for fiuxing thebinder, and means for transposing said particles within the binder byimpressing audio frequency oscillations upon said circuit.

10. A device for recording audio frequency oscillations comprising anelectro-magnet, a circuit for controlling the field of the magnet, meansfor passing through said field a metal strip coated with a bindercontaining magnetically permeable particles, means for transposing saidparticles within thebinder by impressing audio frequency oscillationsupon said circuit, and means for hardening the coating when theparticles are transposed.

Signed at New York in the county of New York and State of New York this13th day of July A. D. 1931.

SAMUEL RUBEN.

